This application relates to a one-part polyurethane based adhesive useful in bonding porous and nonporous materials. The adhesive is especially useful in bonding glass into window frames, for example windshields into automobiles.
Polyurethane adhesive compositions typically comprise at least one urethane prepolymer. Adhesives useful for bonding to nonporous substrates, such as glass, to metal, are well known. When glass is installed in automobiles on a production line, a one-part moisture curable polyurethane adhesive is preferably used, as the equipment needed for the application of such an adhesive in an automobile assembly plant is less expensive than the equipment needed to apply a two-part adhesive. One-part polyurethane adhesives are disclosed in U.S. Pats. No. 4,374,237 and 4,687,533 incorporated herein by reference.
In the automotive after market replacement industry, glass is often bound into automobiles through the use of two-part moisture curable polyurethane adhesives. Two-part polyurethane adhesives are used because they offer rapid initial cure allowing for rapid drive-away times. Two part adhesives require special applicators which mix the two parts in specific proportions immediately prior to application. These applicators are more difficult and costly to use than applicators used for one-part adhesives. Further, the improper application or mixing of two part adhesives can result in poor adhesion. Two-part polyurethane adhesives are well known, U.S. Pat. No. 4,835,012, incorporated herein by reference, and DE 4,210,277.
In addition the market demands simpler application systems and faster curing adhesives which allow even faster drive away times. If the adhesive cures too rapidly, then the window installer loses the necessary time to install and properly place the glass into the frame before the adhesive becomes too intractable to work with. Working time is defined as the period from application of adhesive until the adhesive becomes too intractable to work with.
Future regulations in the U.S. will require dual airbags in vehicles. During crashes the airbags inflate and exert additional pressure on the windshield. Federal Transportation Agency regulations require that windshield remain in place at crashes of up to 30 mph (48 KPH). This requires adhesives which have enhanced strength at the drive away time. To meet such a standard, the lap shear strengths of the adhesive should be preferably 150 psi (1033 kPa) or greater as determined according to ASTM D-3163 and demonstrate impact energy strength of 9 ft-lbs (12.2 Joules) or greater at the designated drive away time.
Therefore, what is needed is a one-part polyurethane adhesive which facilitates faster drive away time, which meets the strength and impact requirements defined above and which still provides for a reasonable working time to facilitate proper placement of glass in window frames. What is also needed is a one-part system which meets these requirements so that the disadvantages of the two-part systems can be avoided.